The preparation of reaction injection molded (RIM) elastomers such as non-cellular, rigid polyisocyanurate products is known and has become popular for the preparation of automobile body parts and other applications. Generally, the commercial RIM machines are of the two stream variety to prepare the reacted products, however three, four or more reactive streams may be employed. The preparation of polyisocyanurate resins using a wide variety of trimerization catalysts is also known.
Rigid non-cellular RIM compositions from polyether polyols, isocyanates and organic carbonates are known using various modifiers and catalysts. The preparation of laminated composites is also well known and the laminates may contain such materials as metal, wood or other cellulosic material, plastic, glass, or ceramics. These resins may also be filled with fibers of these materials to add structural strength.
These reinforced resin components, also called structural RIM or SRIM, are also used in the automotive industry as substances to replace metal. ARSET.RTM. HI 2801 and ARSET HT 3500 resins are used to give polymers with high elongation, according to U. E. Younes, "Resins Resist Impact: Versatile SRIM Composites," Urethanes Technology, June/July 1990, pp. 20-23. RIM compositions using these resins which contain a soluble adduct of a tertiary amine and a cyclic alkylene carbonate as a catalyst are described in U.S. Pat. Nos. 4,709,002; 4,731,427; 4,757,123; 4,800,058; 4,879,164; and 4,886,700.
The advantages of ARSET formulations include quick cure rates at room temperature coupled with low viscosity. These properties are particularly important when molding large RIM parts. The low viscosity of the system translates to effective wetting of glass reinforcements. The low viscosity components can easily penetrate the glass mats, allowing for higher glass loadings, which impart better performance properties. The fast reactivity signifies that the material has sufficient time to flow into the mold, but at the onset of the isocyanurate reaction, the cure rate is very fast. This, in turn, permits quick demold of parts and high production rates.
The reaction rates of these polyurethane systems are dependent upon the amount of catalyst. However, a practical limit is reached at the amount of catalyst required to give the desired cure rate and polymer properties. It is important that the mold be filled completely before cure begins. In many cases for large RIM parts, it is desirable to increase the set time to facilitate mold filling, while at the same time not affecting the cure rate adversely. Too long of a delay, however, can result in undesirably long total mold times.
As will be explained, the invention herein involves the careful use of amino acid salt catalysts having the formula: ##STR2## where R and R' are independently hydrogen or alkyl having 1 to 12 carbon atoms; where R" are independently alkylene groups having from 1 to 4 carbon atoms; where M is an alkali metal; and where x ranges from 1 to 2.
Amino acid salts of this group are known materials and are commercially available as part of a solution with diethylene glycol as CURITHANE.RTM. catalysts from Air Products and Chemicals, Inc. Curithane products may also posses acid-containing isocyanate catalysts. Indeed, the amino acid salt defined above is only known as a co-catalyst with other catalytic compounds, and then these co-catalyst combinations are only known for the trimerization of polyisocyanates to polyisocyanurates in rigid foam systems, not for use in non-cellular RIM systems. Representative patents describing these co-catalyst combinations for cellular rigid polyisocyanurate foams include U.S. Pat. Nos. 4,101,465; 3,896,052 and 4,011,180; 3,903,018 and 3,986,991. These patents are incorporated by reference herein for further details.
Additionally of interest is U.S. Pat. No. 3,580,868 which describes that synthetic resins, especially cellular foams, may be prepared by the polymerization of compounds which contain more than one isocyanate group in the molecule, in the presence of Mannich base catalysts which are obtained by reaction between dimethylamine, formaldehyde and phenols which contain in the molecule at least one organic substituent which has at least 6 carbon atoms. Less than equivalent quantities of compounds which contain active hydrogen atoms and the usual auxiliary agents may be optionally present. Also by way of general background in this area is Y. Imai, et al., "Trimerization Catalysts for Isocyanurate Foams," European Journal of Cellular Plastics, October 1980, pp. 126-133, which decribes various catalysts suitable for isocyanurate foams, but not for non-cellular RIM materials.
As noted, it would be an improvement in the art if the reactivity of the various RIM systems could be slowed without affecting the cure rate. This would permit the components to be completely injected into a large mold prior to the cure, though the cure rate itself would desirably remain quick. Such an improved system would maximize the production of quality RIM parts at high rates.